Stop motion switches of various known constructions are used to monitor the continuity of elongated filaments, a thread or yarn as such thread or yarn is continuously supplied to a textile machine, e.g., a knitting machine. Examples of such known constuctions are disclosed in the following U.S. Pat. Nos. 4,075,445; 3,521,265; 2,963,890; 2,825,119; 2,801,307; 2,689,393; 1,784,560; 1,721,291; and 1,423,398. U.S. Pat. No. 1,721,292 is a typical example of the prior art type switch construction and comprises a contact plate adapted to come in contact with a bus bar to complete an electrical circuit. The contact plate is held out of contact with the bus bar by a filament threaded through an eyelet forming a part of the contact and upon breakage of the filament the contact comes in contact with the bus bar closing a circuit and thus de-energizes a textile machine to which the filament was being fed. Here, as in other prior art switches, which perform the same function, the electrical and mechanical engagement between the contact and bus bar is always in essentially the same confined area.
Any textile environment is almost always subject to dust particles and oil having the inherent tendency to accumulate on the very area where electrical contact is made in stop motion switches. It takes only a minor accumulation of dust, oil or a mixture of the two in this vital area to cause a short, thus causing a failure of the switch to perform its intended function, i.e., de-energize a knitting machine when a break in the continuity of the filament being fed into the textile machine occurs. It is towards the solution of this problem that this invention is directed.